Investigations are designed to learn more about the cellular control and transport of mineral ions which become incorporated in developing enamel and defensive mineralization of primary dentin. Maturative ameloblasts of fluorotic rats contain intracellular deposits of crystalline mineral. Injected cobalt causes a temporary reduction or cessation of mineral ion transport into a forming enamel front. These experimental models will be used to trace the pathway of mineral ions as they pass from tissue fluids to mineralizing enamel utilizing electron microscopy, histochemistry and electron microscopic autoradiography. Defensive mineralization of rat molar primary dentin will be further analyzed. The enamelfree region of dentin will be examined microradiographically and electron microscopically before and after eruption of the tooth to ascertain the rate and pattern of intratubular mineralization. The pathway of calcium and matrix precursors will be traced during periods of active intratubular mineralization utilizing light and electron microscopic autoradiography. Movements of organic and inorganic components will be correlated with development of tubular occlusion with the objective of determining cellular involvement in this process.